Carpenters must frequently join materials at an angle in a manner commonly known as a mitre or coped joint. A mitre joint typically consists of two pieces of material that are joined at a corner, where each of the pieces is cut at a bisecting angle of the corner shape requiring the mitre joint. Mitre joints are used on molding surrounding doors, windows, floor bases, and stair cases as well as in other locations. As doors, windows, walls, and staircases are frequently not perfectly square due to natural imperfections, the actual angle required for the mitre joint must first be determined and then the materials cut to this angle.
Problems exist with current methods with regards to translating the measured mitre angle into a finish cut on the material to be joined. Imprecision between the scales of the device used for measuring the required mitre angle and of the cutting apparatus can result in inaccurate mitre cuts, resulting in mitre joints that are not mated properly. Also, human imprecision is added when the operator must read one scale on the measurement device and transfer the value to another scale on the cutting machine.
For many years, baseboard moldings, chair rail molding, cornice molding, etc. have been cut on a fixed mitre box. Some of the known fixed mitre boxes were manufactured from wood, steel, aluminum, or plastic. Fixed mitre boxes are virtually useless in making most angled mitre cuts accurately. In addition, the fixed mitre boxes only include precut mitre angle slots designed to cut 45, 60 and 90 degree angles. After several cuts through the same precut angle slot on a fixed mitre box, the angle slots become wider and wider until it is impossible to cut an accurate mitre.
More recently, circular adjustable angle mitre saws and radial arm saws have been used for cutting mitre angles. The latest generation of circular adjustable mitre saws also includes laser projection of the saw blade plane in attempt to guide the user in making more precise cuts. Prior to the use of the circular adjustable angle mitre saws, a pivoting manual saw was also used for cutting mitre angles.
Adjustable angle saws, both circular and manual, and radial arm saws still require that one first determine the angle of the corner in degrees and then set the mitre saw at the proper mitre cut line. If one does not accurately determine the angle of the corner in degrees, then the mitre cut will be incorrect and the piece of cut molding will be scrap material. Thereafter, the person making the mitre cuts must proceed to make further adjustments on the degree cut line with the hope that eventually an accurate mating joint will be cut.
It has always been an educated guess to determine the inside or outside angle of room corners in degrees, which is followed by a few trial and error cuts until one achieves an accurate mitre joint. The intersecting walls forming room corners should be 90 degrees, however, in many wall constructions this may not be entirely true. In fact, the room corners may often be up to 2 or 3 degrees off square. Consequently, if one cut perfect 45 degrees intersecting mitre cuts, the cut pieces of molding would not mate accurately.
As shown in FIG. 13, up to the present time, a very tedious and time consuming method used to determine a mitre cut without estimating or otherwise guessing at the angle of the corner is to use a 3″ or 4″ wide board placed flat on the floor against one wall and scribe a line on the floor away from the corner along the outside edge of the hoard. The same tedious method would then need to be performed on the other wall to scribe a line intersecting the scribe line from the first wall. The line drawn from the corner of the wall to the intersecting scribe lines on the floor is the mitre cut line that one would then need transfer to the saw deck using an adjustable square with or without an angle scale in degrees. A more tedious method of cutting 90 degree inside corner mitres was to trace the molding scroll pattern on one member and cut out the scroll pattern with a coping saw to mate with the other member. This method could only be used on 90 degree inside corners.
Because of the difficulty in judging the proper angles for the mitre cuts, one would be forced to make multiple cuts to arrive at accurate mating mitres, or simply caulk the inaccurate mitre to cover up a bad mitre joint.
The national average for carpenter wages is estimated to be about $30 per hour. Inaccurate mitre cuts result in increased labor costs and wasted material, which severely affect the profitability of a particular construction job for the carpenter. In addition, the wasted wood material also has a detrimental impact on the environment.
What is still needed in the art is a tool to accurately and easily determine the proper molding mitre cut plane without the need for measuring angles in degrees in order to achieve accurate and precise mitre cuts for both inside and outside corners.